1. Field of the Invention
The present invention relates to a method for producing nonionic detergent granules. More specifically, the present invention relates to a method for producing nonionic detergent granules comprising a nonionic surfactant as a main surfactant component and having a small compositional restriction, a high bulk density, and excellent powder fluidity properties and non-caking property, and being free from exudation.
2. Discussion of the Related Art
As for a method for producing powdery detergent composition containing a nonionic surfactant, a method for producing granular detergent composition comprising the steps of preparing a nonionic surfactant in a detergent slurry, and spray-drying the resulting mixture has been proposed However, in this method, besides having a large facility cost and large consumption of energy, the nonionic surfactant decomposes by a hot air upon drying, thereby making it likely to cause problems in the generation of contaminous materials, lowering of a nonionic surfactant content, and deterioration in the surfactant properties. In order to solve these problems, the kinds and amounts of the nonionic surfactants have to be limited (Japanese Patent Laid-Open No. 61-85499), or additives not contributing to washing performance have to be blended (Japanese Patent Laid-Open No. 56-22394).
Japanese Patent Examined Publication No. 60-21200 discloses a method comprising preparing builder base beads by using a spray-drying method, and carrying a nonionic surfactant on the builder base beads. However, in this method, since an anhydrous phosphate builder is used as a builder base, the main builder base is limited only to produce phosphorus-containing detergents, so that phosphorus-free detergents cannot be produced. Also, the process of producing the builder base beads having both a porous outer surface and internal skeleton structures is quite complicated.
Also, Japanese Patent Examined Publication No. 61-21997 discloses a method for continuously producing a granular detergent, comprising the steps of hydrating and wetting a washing active salt using an agglomeration device, stirring the wetted washing active salt in a tightly sealed container, impregnating with a nonionic or anionic surfactant, and drying it, to thereby give a granular detergent free from caking even after a long-term storage. However, in this method, since the agglomerates of the hydrated and wetted washing active salt are impregnated with a surfactant, a drying process has to follow granulation, thereby making the process complicated. Also, the proportion of the nonionic surfactant to be blended in the composition depends greatly upon the properties of the agglomerated granules. Therefore, when the proportion of the nonionic surfactant is made high, agglomerated granules having high oil-absorbing properties have to be prepared, thereby making the amount of an anhydrous detergent surfactant salt contained in the composition undesirably large. In other words, the compositional restriction of the detergent granules is large. In addition, the operation upon production such as hydration conditions and drying conditions becomes undesirably complicated.
Japanese Patent Laid-Open No. 3-26795 discloses a method for producing a granular detergent having good fluidity property, solubility, and dispersability, comprising the steps of forming zeolite agglomerates comprising a zeolite, a filler, and a water-containing binder using an agglomerate-forming device, further forming detergent agglomerates comprising the above zeolite agglomerates and surfactant-containing detergent components, and drying the detergent agglomerate. However, in order to obtain detergent agglomerates, the production steps at least comprise five steps, making the entire process quite complicated. Also, since it is essential to form agglomerates having zeolite as a main component, there arises such problems that the compositional restriction of the detergent granules is made large.
Japanese Patent Laid-Open No. 62-263299 discloses a method for producing a granular detergent composition comprising the steps of uniformly kneading a nonionic surfactant and a builder to form a solid detergent, and then disintegrating the solid detergent. However, in this method, it is difficult to obtain nonionic detergent granules having good fluidity property, and large amounts of undesirable fine particles are produced. Further, the total amount of zeolite and light sodium carbonate has to fall in the range of from 50 to 80% by weight, thereby making the compositional restriction for blending in nonionic detergent granules large. In addition, Japanese Patent Laid-Open No. 61-89300 discloses a method for producing a nonionic surfactant-containing granulated product, comprising the steps of blending a water-soluble granule powder and a silica powder, spraying a nonionic surfactant to the above mixture, and adding a zeolite or calcium carbonate powder to the resulting mixture. However, in this method, since the powder is tumbled and granulated using a drum-rotatable granulator, it is impossible to produce a nonionic surfactant-containing granulated product having a high bulk density.
Also, Japanese Patent Laid-Open No. 5-209200 discloses a method for producing a nonionic surfactant-containing granulated product, comprising the steps of agitating and blending a mixture of detergent starting materials containing a nonionic surfactant as a main surfactant component in an agitating mixer, the agitating mixer containing an agitating shaft along the center line of the inner portion, agitation impellers arranged along the agitating shaft, and a clearance formed upon rotating the agitating impellers between the agitating impellers and a wall of the agitating mixer, to thereby form a layer of the detergent starting materials adhered to the wall of the agitating mixer; and granulating the obtained mixture while increasing the bulk density of the detergent starting materials by the agitating impellers. However, since the nonionic surfactant is supported by the capillary force or the surface adsorption of the powdery starting materials, the supporting force is weak, so that sufficient adhesion of the nonionic surfactant-containing powder to the equipment upon conveying or sufficient exudation inhibition when packing the powder in a paper box container cannot be achieved. In addition, Japanese Patent Laid-Open No. 4-227700 discloses a powdery detergent prepared by spraying a nonionic surfactant to spray-dried particles containing an anionic surfactant and a soap. However, in this method, the nonionic surfactant cannot be blended in a large amount, so that exudation is undesirably likely to take place.
Also, Japanese Patent Examined Publication No. 52-30962 discloses a method for producing a powdery heavy detergent comprising the step of neutralizing a fatty acid or a nonionic surfactant-containing fatty acid with hydrated powdery sodium carbonate having a water content of not more than 20% in a temperature range of from a temperature not less than the melting point of the fatty acid to 100.degree. C. However, since the nonionic surfactant is not contained in a large amount, detergent granules containing a nonionic surfactant as a main surfactant component cannot be produced. Therefore, detergent granules having high bulk density cannot be obtained in this method. Moreover, since builder components are not blended, the compositional restriction in the detergent becomes large.
Japanese Patent Unexamined Publication No. 6-507197 discloses that at least one of polyethylene glycols, copolymers of maleic anhydride and ethylene, nonionic surfactants, glycerol ethers, and fatty acids can be used in binders for granular composition. However, the reference simply discloses that each of the above components can be used for the granular composition, and it is silent in the teaching that an alkalizer, a fatty acid (an acid precursor of an anionic surfactant capable of having a lamellar orientation), and a nonionic surfactant are combinably used. Also, it never suggests or teaches the formation of a gelated product with the nonionic surfactant and the effects achieved thereby.